IP Down to the Field Level Single Pair Ethernet in System Integration

In design-in projects for Single Pair Ethernet, it is often assumed that the technology can be integrated as an additional interface into existing systems. In practice, however, it quickly becomes apparent that this assumption leads to problems: Without a consistently coordinated system design, stable connections at the field level are hardly achievable.

In automotive or industrial applications, the need to consistently network sensors and actuators on an IP basis is growing. Single Pair Ethernet (SPE) offers a promising approach for this, as data and power can be transmitted over a single pair of wires, enabling the connection of distributed or hard-to-access components.

In practical implementation, however, it quickly becomes apparent that introducing Single Pair Ethernet (SPE) is far more complex than initially assumed. Many companies underestimate the systemic nature of the technology. Instead of merely adapting interfaces, SPE requires a fundamental rethinking of the entire system architecture—from physical transmission and power supply to integration into existing networks. EMC influences, thermal requirements for PHYs and voltage converters, proper differential signal routing, PoDL power concepts, and the parallel coexistence with existing fieldbuses significantly determine stability in later operation. Only when hardware, firmware, power supply, cable quality, and mechanical integration are considered collectively from the very beginning can the potential of SPE be effectively realized in industrial practice.

Typical Sources of Error in SPE Integration

Single Pair Ethernet is often considered a "drop-in replacement" for existing communication solutions—and this is exactly where one of the fundamental misconceptions lies. While traditional fieldbuses are often robust against physical imperfections, SPE reacts significantly more sensitively to deviations in the overall system.

A recurring problem is the inadequate control of impedance along the entire transmission path. Even small discontinuities, such as those caused by unsuitable connectors or layout errors, lead to reflections that can massively impair signal quality.

Another critical point is the power supply via Power over Data Line (PoDL). In many projects, the power budgeting is set too optimistically. Cable lengths, temperature dependencies, and dynamic loads are not sufficiently considered, leading to unstable operating conditions. The integration into existing architectures is also often underestimated. SPE is viewed in isolation, without analyzing its impact on existing fieldbuses, industrial Ethernet networks, and control systems. The result is complex transitional solutions that are difficult to maintain in the long term. These challenges are particularly evident in real applications—for instance, in IP-based sensor connectivity in large-scale facilities or distributed automotive systems.

Use Case Automotive: IP-Based Actuator Control via SPE

In a development project in automotive engineering, the control of several decentralized actuators in a commercial vehicle was to be reimplemented. Such decentralized actuators are typically found in vehicles in valve and flap controls, smaller electric drives, thermal management systems, or smaller electric drives for auxiliary units. The goal was to replace existing bus-based communication solutions with a seamless IP-based architecture to enhance diagnostic functions and enable more flexible system integration—such as for over-the-air updates.

The actuators were distributed throughout the vehicle and partially located in space-critical areas. In vehicles, this typically includes the engine compartment or areas near power electronics. At the same time, there was a requirement to reduce wiring complexity and save weight. Against this backdrop, the decision was made to use Single Pair Ethernet to transmit data and power through a minimized cable design.

Significant problems arose as early as the initial prototype phase. Electromagnetic interference from neighboring power components such as inverters and DC/DC converters led to unstable communication. Additionally, challenges emerged in power supply via PoDL: voltage drops during load changes of actuators, such as when adjusting flaps or valves, caused unexpected resets of individual nodes. Another critical factor was cable routing in the vehicle. Different cable lengths, contact resistance at connectors, and mechanical stresses from vibrations affected signal quality more than initially anticipated. Such effects can be further exacerbated in vehicle applications due to vibrations or thermal stresses. A stable solution was only achieved through a holistic system optimization. This included an EMC-compliant design of cable routing, the targeted selection of automotive-grade SPE cables and connectors, a robust PoDL configuration with sufficient reserves, and an adapted hardware and firmware implementation for actuator controls.

The result is a future-proof, IP-based communication architecture in the vehicle that not only ensures reliable control of the actuators but also enables advanced diagnostic and update functionalities—with reduced cabling effort, lower system complexity, and simultaneously higher requirements for system design.

SPE Integration: How Stable Systems Are Created

The key to successful SPE projects lies in a consistent system-level approach from the very beginning. This includes, in particular, close integration of hardware, software, and system development. In the conceptual phase, cable lengths, topologies, data rates, and power requirements should be clearly defined. Based on this foundation, suitable PHYs, cables, and connectors can be selected.

A comprehensive EMC concept is essential, with simulations and pre-compliance measurements helping to identify potential weaknesses at an early stage. Equally important is a realistic design of the power supply, taking worst-case scenarios into account. Moreover, integration into existing systems should be planned early on. Hybrid architectures, where Single Pair Ethernet operates parallel to traditional fieldbuses, are often the standard in practice.

Electromagnetic compatibility is particularly critical, playing a central role in SPE. Due to transmission over a single pair of wires, the inherent symmetry of multi-pair systems is lacking, making SPE systems more sensitive to common-mode interference and external radiation. Typical sources of interference include frequency converters, switching power supplies, or long, parallel power lines. These can induce disturbances that directly affect signal quality. To mitigate these effects, several measures are required. A key factor is clean differential signal routing in the PCB layout with controlled impedance. Additionally, suitable common-mode chokes and filters must be used to suppress interference.

The choice of the right cables is also crucial. Shielded cables with defined transmission properties contribute significantly to stability. The shield connection must be correctly implemented on both ends to ensure effective dissipation of interference. Lastly, mechanical integration is also relevant, as cable routing, distances from interference sources, and the grounding concepts of the entire system significantly influence EMC performance.

What Single Pair Ethernet Can Achieve—and Where the Limits Lie

Single Pair Ethernet offers three key advantages: seamless IP communication down to the field level, reduced cabling, and enhanced diagnostic capabilities. A major benefit lies in uninterrupted data communication without protocol breaks: sensor data can be directly transmitted to higher-level systems, simplifying network architecture and avoiding media disruptions.

In addition, SPE enables higher data rates as well as the transmission of extensive diagnostic data. This forms the basis for condition monitoring, predictive maintenance, and data-driven optimization approaches. At the same time, transmission over a single pair of wires reduces cabling effort and allows for more compact devices. This results in clear efficiency advantages, especially in modular systems, large-scale infrastructures, or retrofit projects.

Despite these advantages, SPE has not yet been widely adopted in the industry. A key reason for this is cost: SPE components—particularly PHYs, connectors, and specialized cables—are often more expensive than established fieldbus solutions. Additionally, the high development effort plays a role. The necessary system optimization, especially regarding EMC and power supply, leads to longer development times and higher engineering costs.

Another factor is the existing installed base. Many companies have proven fieldbus systems that function reliably. The economic pressure to replace these systems in the short term is often low. Standardization and interoperability are also still partially under development. Different connector interfaces, cable solutions, and implementation approaches complicate widespread adoption. Lastly, many companies still lack experience with SPE, which raises the barrier for embarking on new projects.

System Integration as the Key to Stable SPE Communication

The stability of SPE arises from the close interaction of all system components. This is due to the shared transmission of data and power over the same pair of wires: interference, voltage drops, or impedance mismatches directly impact signal quality and communication stability. Individual optimizations are therefore ineffective if adjacent areas are not consistently designed. Physics, power supply, layout, firmware, and mechanical integration are functionally interconnected. Changes in one of these areas thus directly influence the overall system behavior. Especially in industrial environments with high EMC loads, it becomes evident that only a holistically developed system can function reliably in the long term.

Against this backdrop, it can be beneficial to involve specialized development partners at an early stage. Especially with limited internal resources or a lack of system experience, this can help avoid common mistakes in the early project phases and shorten development times. Particularly under complex conditions—such as long cable lengths, hybrid architectures, or high EMC requirements—external expertise can help prevent design errors and reduce iteration cycles.

Because what matters is not the individual technology but its consistent integration into the overall system. Only when all relevant influencing factors are taken into account early on can SPE be reliably operated under real-world conditions. 

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*Jörg Klenke is a member of the management board and PMO at Burger Engineering